We’ve lost count of the times Hermione Granger ran to the library to consult a book on something mid-conversation.

However, we have kept count of the times books saved the day. Here they are, one dusty tome at a time.

An enormous old book – title unknown

When the trio first stumbled across Fluffy the three-headed dog, Hermione noticed that he was guarding a trapdoor. After Hagrid accidentally mentioned the name Nicolas Flamel, she insisted they spend as much time in the library as possible trying to connect the name with whatever Fluffy was guarding. Without this book, they may not have found the Philosopher’s Stone.

Hermione jumped to her feet. She hadn’t looked so excited since they’d got back their marks for their very first piece of homework. ‘Stay there!’ she said, and she sprinted up the stairs to the girls’ dormitories. Harry and Ron barely had time to exchange mystified looks before she was dashing back, an enormous old library book in her arms. ‘I never thought to look in here!’ she whispered excitedly. ‘I got this out of the library weeks ago for a bit of light reading.’Harry Potter and The Philosopher’s Stone

Magical Mediterranean Water-Plants and Their Properties

When Barty Crouch Jr posed as Mad-Eye Moody he tried to tell Harry about a plant that would allow him to breathe underwater during the Triwizard Tournament. Even though it was technically Dobby who introduced Harry to Gillyweed, Crouch explained that he tried to send Harry the book:

‘Did you realise the book you needed was in your dormitory all along? I planted it there early on, I gave it to the Longbottom boy, don’t you remember? Magical Mediterranean Water-Plants and Their Properties. It would have told you all you needed about Gillyweed. I expected you to ask everyone and anyone you could for help. Longbottom would have told you in an instant.’Harry Potter and the Goblet of Fire

Most Potente Potions

This is the book that, indirectly, gave Hermione ears, whiskers and a tail, and helped Ron and Harry to infiltrate the Slytherin common room. It details how to brew Polyjuice Potion – something any student could learn if they could get a teacher, like Professor Lockhart for instance, to sign it out of the Restricted Section for them with a note…

Madam Pince held the note up to the light, as though determined to detect a forgery, but it passed the test. She stalked away between the lofty shelves and returned several minutes later carrying a large and mouldy looking book. Hermione put it carefully into her bag and they left, trying not to walk too quickly or look too guilty.Harry Potter and the Chamber of Secrets

The Tales of Beedle The Bard

When Dumbledore left this little book to Hermione, it seemed like an innocuous present. Actually it had a vital clue – a strange symbol scribbled inside the cover. Recognising it from a necklace worn by Xenophilius Lovegood, Luna’s dad, Hermione, Ron and Harry paid him a visit to find out what it meant.

Before Mr Lovegood betrayed the trio to the Death Eaters, they read the book and learnt about the Deathly Hallows. Harry later realised that the Elder Wand – the wand from the story – belonged to Dumbledore before he died. This knowledge helped him to defeat Voldemort during the Battle of Hogwarts.

Advanced Potion-Making by Libatius Borage

We’re looking at one particular copy of this Potions textbook here: the one belonging to the Half-Blood Prince. When this little gem fell into Harry’s hands, he couldn’t believe his luck. It transformed him into a Potions superstar and further cemented his status as one of Professor Slughorn’s favourite students.

With this book, Harry nearly killed Draco Malfoy using the sinister spell ‘Sectumsempra’ which he found inscribed in the margins. More happily, it helped him to do so well in Potions class that he won a little bottle of Felix Felicis, or ‘liquid luck’. Once he had swigged some of this potion, Harry managed to sneak out of the castle and extract a very important memory from Slughorn at Dumbledore’s request. This was utterly crucial, because it confirmed Dumbledore’s theory about the Horcruxes keeping Voldemort immortal.

A Very Old Library Book – title unknown

It’s not like Hermione Granger to deface a book but in this case it was very lucky she did. When poor Hermione got Petrified trying to reveal who opened the Chamber of Secrets, Harry and Ron went to visit her in the hospital wing. That was when Harry spotted a piece of crumpled paper in her hand. It was a page torn from a very old library book.

‘Of the many fearsome beasts and monsters that roam our land, there is none more curious or more deadly than the Basilisk.’Harry Potter and the Chamber of Secrets

Tom Riddle’s Diary

Technically, this book turned out to be a Horcrux, but if we overlook that for a moment, it did help Harry to unravel the secrets of the Chamber.

‘I can show you if you like,’ came Riddle’s reply. ‘You don’t have to take my word for it. I can take you inside my memory of the night when I caught him.’Harry Potter and the Chamber of Secrets

Without Riddle’s memory, Harry might not have found out that Hagrid was accused of opening the Chamber the first time around or got the message to ‘follow the spiders’. All this information led to Harry working out the identity of the student killed by the Basilisk in Riddle’s time, discovering the entrance to the Chamber and saving Ginny Weasley’s life.